Can Lynx Survive Global Warming?

The intimate relationship between the Canada lynx and the snowshoe hare has been recognized for a long time. Nearly 100 years ago, naturalist Ernest Thompson Seton wrote, “Of all the Northern creatures, none are more dependent on the Rabbits than is the Canada lynx. It lives on Rabbits, follows the Rabbits, thinks Rabbits, tastes like Rabbits, increases with them, and on their failure dies of starvation in the unrabbited woods."

Indeed it does. Snowshoe hare populations rise and fall on a regular 10-year cycle, and when they crash, “life becomes hell for the lynx,” says Stan Boutin, a biologist at the University of Alberta who studied lynx for the past 11 years. Boutin and his colleagues are adding a new wrinkle to old knowledge, tying the fate of the animals to a more recently discovered conservation issue—global warming.

The lynx ranges throughout the boreal forest that stretches across much of Canada and Alaska. The cat also makes rare appearances in the Lower 48, usually in more mountainous areas. A relative of the bobcat, the lynx’s most distinctive features are its short, black-tipped tail and tufted ears. Its oversized paws help it run on snow. During the peak hare population, when their numbers may increase 50-fold over the low population, a lynx may eat one hare a day. Other predators, including owls and foxes, also feed on hares—at least 95 percent of snowshoes that die when numbers crash are killed by predators.

Boutin and his colleagues have discovered that the lynx population that spans Canada is actually divided into three genetically distinct subpopulations. Those in the West are isolated by the Rocky Mountains from those in the East, while their eastern kin are broken into two groups, the genetically distinct continental population of central and northern Canada and the Atlantic population of Canada south and east of Hudson Bay. These two eastern groups are separated by an invisible barrier that Boutin and other researchers are starting to reveal: climate.

The distinct areas the two eastern populations roam are influenced by variations in a weather pattern, called the North Atlantic Oscillation (NAO), that affects climate in the North Atlantic much as El Nino affects it in the Pacific. Fluctuations in the NAO can cause chilling and warming periods, making snow crusty on top or keeping it fluffy and light. These changes in snow condition are critically important to lynx, Boutin says. The cats in the Atlantic population live in an area where the snow tends more often to be crusty, an advantage to the lynx, because they can run along the surface in pursuit of hares. The continental population has to contend with snow that is more often fluffy, a distinct advantage to the hares, which are light enough to skim the surface while lynx bog down.

These differences in snow cover actually affect lynx genetics, because lynx that grow up in fluffy snow areas want, as adults, to stay in fluffy snow areas, and crusty-snow lynx feel the same way about their natal homes, Boutin says. As a result, gene flow between the continental and Atlantic populations is restricted.

When the hares decline from their peak numbers, they leave a lot of hungry, vulnerable predators behind. Even when snowshoes are at a high, life for the lynx isn’t all that easy—70 to 80 percent of them live only two or three years. When the hares nosedive, lynx face harsh new realities. They may even be hunted by larger predators. Only lynx with the most finely honed hunting skills are likely to survive the dearth of hares and make it to the next upward swing in numbers.

Global warming may add a painful new twist to this equation. Increasing numbers of warming spells will render snow crusty more often than happens now, making the hunting easier for lynx used to crust. Fluffy-snow lynx may have to develop new skills, however, which could be a behavioral burden for them. Moreover, increased lynx hunting success could influence subtly the hare cycle in ways good for neither lynx nor hares. “This lynx-hare cycle is an amazing phenomenon,” says Boutin. “It has proved to be a very robust relationship that has sustained both species for thousands of years. If we start to get climate warming and a crusting of snow without long, deep, cold spells, it could change the interaction and disrupt this robust system. It’s one more way in which global warming is giving us an ecological warning.”

Roger Di Silvestro is a senior editor for this magazine.

Habitat Where U.S. Lynx Roam

Biologists know little about Canada lynx range south of the border, where the cat is a threatened species. In the Lower 48, the lynx historically was most numerous in New Hampshire, Minnesota, Montana and Washington. New studies confirmed that Maine hosts a population of the cats and found evidence of lynx in Idaho, Wyoming and Utah, although those animals may have been transients, rather than part of a permanent population.